Jean-Thomas Larkin is Andrew "Andy" Larkin's non-existent long-lost brother who allegedly grew up speaking French in Montreal.
When Andy was grounded for an unsuccessful prank, Jennifer "Jen" Larkin told him that no girl would be seen dead with him, so he decided to date Lauren "Lori" Mackney. However, all his schoolmates resented him since the prank he got grounded for, so he put on a beige jacket that was too big for him, sunglasses and a long brown wig and spoke in a French accent throwing in some French and fake-French words into his speech and pretending not to be a native English speaker. When Lori wasn't convinced, Andy photoshopped himself with himself as Jean-Thomas and recorded his voice over the phone. This convinced Lori that Jean-Thomas existed and she got a crush on him, which scared Andy as his crush had a crush on a non-existent version of himself, so he as Jean-Thomas decided that he'd stolen at age six, committed vandalism at age eight and mooned an Australian tourist at age eleven.